Diabetes is a major public health concern because of its increasing prevalence and associated health risks. The disease is characterized by high levels of blood glucose resulting from defects in insulin production, insulin action, or both. Two major forms of diabetes are recognized, type I and type II. Type I diabetes develops when the body's immune system destroys pancreatic beta cells, the only cells in the body that make the hormone insulin that regulates blood glucose. To survive, people with type 1 diabetes must have insulin delivered by injection or a pump. Type II diabetes accounts for about 90 to 95 percent of all diagnosed cases of diabetes. Type II diabetes usually begins as insulin resistance, a disorder in which the cells do not use insulin properly. Key target tissues, including liver, muscle, and adipose tissue, are resistant to the effects of insulin in stimulating glucose and lipid metabolism. As the need for insulin rises, the pancreas gradually loses its ability to produce insulin. Controlling type II diabetes with medication is essential; otherwise it can progress into pancreatic beta-cell failure requiring complete dependence on insulin.
Obesity increases the risk of type II diabetes as well as many other health conditions including coronary heart disease, stroke, and high blood pressure. More than one-third of U.S. adults (over 72 million people) and 17% of U.S. children are obese. During 1980-2008, obesity rates doubled for adults and tripled for children. During the past several decades, obesity rates for all population groups—regardless of age, sex, race, ethnicity, socioeconomic status, education level, or geographic region—have increased markedly.
Research has identified the enzyme 5′ adenosine monophosphate-activated protein kinase (AMPK) as a regulator of cellular and whole-body energy homeostasis. AMPK is activated by cellular stress resulting in downstream events that serve to conserve or generate ATP. AMPK is composed of three distinct subunits, each with multiple isoforms: the alpha subunit (alpha 1 or 2); the beta subunit (beta 1 or 2); and the gamma subunit (gamma 1, 2, or 3); for a total of twelve possible heterotrimeric isoforms.
In the liver, activated AMPK phosphorylates a variety of substrates including 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (Clarke, P. R. & Hardie, D. G., EMBO J 9, 2439-2446 (1990)) and acetyl-CoA carboxylase (Carling, D. et al. FEBS Letters 223, 217-222 (1987)) which inhibits cholesterol biosynthesis and decreases fatty acid synthesis, respectively. Therefore, activation of AMPK should lead to decreases in the levels of triglycerides and cholesterol. AMPK is also thought to regulate plasma glucose levels by decreasing hepatic gluconeogenesis through downregulation of key gene products following phosphorylation of CRTC2 (Koo S. H. et. Al., Nature 437, 1109-1111 (2005)). In muscle and myocardial tissues, AMPK activates the transport activity of glucose transporter 4 (GLUT4) increasing glucose uptake into cells thereby producing an additional avenue for decreasing plasma glucose (Kurth-Kraczek, E. J. et. al., Diabetes 48, 1667-1671 (1999)). AMPK activation has also been shown to enhance mitochondrial biogenesis improving fatty acid oxidation and decreasing circulating lipids (Merrill, G. M. et. al., Am. J. Physiol. 273, E1107-E1112 (1997)). Direct activation of AMPK using AICAR (5-aminoimidazole-4-carboxamide riboside) has been shown to lead to beneficial effects on several metabolic endpoints including improved glucose disposal, decreased hepatic glucose output and decreases in plasma triglycerides and free fatty acids (Song, X. M. et. al., Diabetologia 45, 56-65 (2002); Bergeron, R. et. al., Diabetes 50, 1076-1082 (2001); Buhl, E. S. et. al., Diabetes 50, 12-17 (2001); Iglesias, M. A. et. al., Diabetes 51, 2886-2894 (2002), Fogarty, S. & Hardie, D. G., Biochim et Biophys Acta 1804, 581-591 (2010)). Because of AMPK's pluripotent effects on carbohydrate, lipid, and cholesterol metabolism and biosynthesis, agents that activate AMPK are attractive therapeutic targets for treating metabolic syndrome disorders such as diabetes, obesity, and dyslipidemia.
Decreases in renal AMPK activation have been implicated in the etiology of diseases of the kidney, including diabetic nephropathy, acute kidney injury (AKI), and polycystic kidney disease (PKD); activation of AMPK through hormonal (adiponectin) or pharmacological (AICAR) mechanisms has been shown to be protective in rodent models of these diseases. In diabetic nephropathy decreased AMPK activation in podocytes occurs early in the disease and is associated with increased expression of the NADPH-Oxidase protein Nox4 and increased proteinuria. These effects were reduced following administration of the AMPK activators AICAR, metformin, and Adiponectin (Lee, M J. et. al. American Journal of Physiology—Renal Physiology. 292. F617-F627 (2007); Sharma, K. et. al. Journal of Clinical Investigation. 118. 1645-1656. (2008)). In ischemia/reperfusion models of AKI the AMPK activators metformin and AICAR were shown to dose-dependently reduce subsequent proteinuria, oxidative tissue damage, and kidney macrophage infiltration (Lempiainen, J. et. al. British Journal of Pharmacology 166. 1905-1915 (2012); Seo-Mayer, P. W. et. al. American Journal of Physiology—Renal Physiology, 301, F1346-F1357 (2011)). In two rodent models of PKD the AMPK activator metformin was shown to reduce renal cyst expansion (Takiar, V. et. al. PNAS 108, 2462-2467 (2011)). These studies suggest a broad benefit of AMPK activators in multiple renal diseases.
The compounds of the present invention activate AMPK and are, therefore, useful in treating metabolic disorders such as diabetes, obesity, and dyslipidemia as well as the renal diseases chronic kidney disease, diabetic nephropathy, acute kidney injury and polycystic kidney disease.